div{
  border: 1px solid;
}
#mainDiv{
  width: 800px;
  height: 400px;
  display: flex;
}
.bookDiv{
  height: 400px;
  width: 400px;
}

#shopDiv{
  width: 500px;
  height: 500px;
  background-color: rgba(255,0,0,0.4);
  position: absolute;
  left: 0;
  top: 0;
  visibility: hidden;
  display: flex;
  align-items: center;
  justify-content: center;

}
#shopContentDiv{
  background-color: wheat;
  width: 600px;
  height: 400px;
}
